A study in the March edition of the Journal of Clinical Endocrinology and Metabolism shows that cocaine use increases the susceptibility for HIV infection by blunting interleukin-6's effects on the body. A study of 30 occasional cocaine users showed that production of IL-6, a chemical that helps coordinate immune system responses to invading pathogens, is significantly inhibited when cocaine is present in the body. This can make HIV infection easier because the immune response would be weakened in the case of exposure to the virus.

"The drug is priming tissue to not fight off infection right at the point when the individual is most in need of a strong immune response," wrote lead researcher John Halpern. It's not clear exactly how much the risk of infection is boosted by cocaine use, but, Halpern added, "if cocaine knocks down the immune system by only 5%, but you add to that poor nutrition and high-risk behaviors, that 5% could put you over the top--and you get HIV." Previous studies have also shown that cocaine use by HIV-positive people significantly speeds up HIV replication in the body and leads to faster progression to an AIDS diagnosis.